1. Field of the Invention
The present invention relates to a fan motor with constant speed control by a microprocessor system, and more particularly to a fan motor whose speed is controlled by a microprocessor system and other peripheral controllers to modulate the drive voltage for the fan, thereby keeping the fan running at a predetermined speed.
2. Description of the Related Art
Heat-dissipating fans are generally used to cool computer systems and electronic equipment thereof to thereby avoid failure of the systems and/or burning of electronic elements due to over-temperature resulting from poor heat dissipation. Acoustic noise is inevitably generated during high-speed operation of the heat-dissipating fan and thus adversely affects the user""s efficiency.
Fan speed must be varied in response to a change in the temperature in the system. System failure and/or burning of electronic elements occur if the change in the fan speed mismatches the ambient temperature. When in a high-temperature ambience and the fan speed is increased too fast and renders sudden reduction in the ambient temperature, the fan speed must be reduced which will cause a rise in the temperature and the fan speed must be increased again. As a result, the fan speed is repeatedly increased and reduced in response to the change in the ambient temperature. Mismatch between the fan speed and the temperature causes a waste in electricity, system failure, and/or burning of electronic elements. It is therefore necessary to develop constant speed heat-dissipating fans to keep the fan running at a constant speed, thereby providing a constant ambient temperature.
A conventional fan motor is shown in FIG. 1 of the drawings that correspond to FIG. 3 of U.S. Pat. No. 5,249,741 to Bistline et al. issued on Oct. 25, 1993. FIG. 1 is a flowchart illustrating how the speed values are determined for each fan. In step 10, the IPLROS (initial program load read only storage) queries the I/O slots to determine what option cards may be in the I/O slots. In step 11, the NVRAM (non-volatile random-access memory) is queried to determine if a previous configuration for the computer is stored there. In step 12, a thermal table is queried to determine the base cooling requirements for each bay of the computer system and the cooling requirements for each of the components. In step 13, the speed value for each of the fans is determined. In step 14, the system configuration including the location of the option cards and the speed values for each fan are stored in NVRAM for future reference. In step 15, the speed values are stored in four bit registers which value is then converted by a digital-to-analog converter into an analog value. In step 16, the current configuration is compared to the previous configuration including location of the various option cards to determine if the configuration has changed.
However, the automatic fan speed control disclosed in U.S. Pat. No. 5,249,741 can only update the thermal table by means of using the operating system to thereby determine the fan speed. Parameters such as fan state, actual speed, and fan speed set-up that may affect control of constant ambient temperature in the system are not taken into consideration.
Other objects, specific advantages, and novel features of the invention will become more apparent from the following detailed description and preferable embodiments when taken in conjunction with the accompanying drawings.
In view of the above drawback, the present invention provides a fan motor that uses parameters of actual speed to determine fan state and speed set-up, thereby outputting a drive voltage with a smooth waveform. The drive voltage allows match between the fan actual speed and the fan state, thereby keeping the fan running at a constant speed.
A fan motor with constant speed control comprises a microprocessor system, a bus control logic, a register for actual fan speed, a register for fan state, a register for speed set-up, a linear variable voltage circuit control logic, and a braking/running enabling control logic. The microprocessor system is connected via the bus control logic to the register for actual fan speed, the register for fan state, and the register for speed set-up. The register for fan state sets up enabling of braking and running by means of controlling output voltage by the braking/running enabling control logic. The register for speed set-up sets up speed values by the microprocessor system. After comparing a speed value to an actual fan speed signal by the linear variable voltage circuit control logic, the linear variable voltage circuit control logic generates a linear variable voltage (drive voltage) which is outputted to the fan via the braking/running enabling control logic. The actual fan speed signal is accumulated in the linear variable voltage circuit control logic and then outputted to the register for actual fan speed for retrieval by the microprocessor system via the bus control logic.